176 AGRICULTURAL REPORT. 



insect-origin of this disease, 'which he cousidored as a kind of fungus. * » * 

 But whether caused by vitiated sap, as Doctor Burnet supposed, or by the irritatiug 

 punctures of iusects, Tvhich is tho iirevailing opinion, they form an appropriate bed for 

 the growth of numerous little parasitical plants of fungi." 



Doctor Fitch claims to have made a careful investigation of this subject, and as his 

 observations are quite accurate wo quote again from his address : " There has been 

 much speculation as to the cause and "true nature of these excrescences. " * 



Most persons suppose them to be of insect origin. The larva? of tho curculio are almost 

 always found in them, and these larvfo consume nearly all the spongy matter of tho 

 warts, but do not touch the little fungus growing on their surface, which remains, 

 forming a kind of shell after the whole inside is devoured. But as these excrescences 

 are sometimes found wholly free from curculio larvaj and all other v/orms, it is obvious 

 they are not tho cause of their growth. * * Suffice it to say that now, 



having carefully examined these excrescences from their commencement onward through 

 their subsequent growth, I am prepared to say, with the fullest confidence, that the 

 microscope shows nothing whatever about them, externally or internally, indicating 

 that an insect has anything to do with causing them." Then, after giving his views as 

 to what constitutes a fungus, he says : " AVe arrive at the conclusion that these excres- 

 cences are not of insect origin, and are not a vegetable fungus, but are iiroperly a 

 disease of these trees, in many respects analogous to tho cancer in the human body." 



Mr. Walsh, whose definition of black-knot wo have already quoted, agrees with Dr. 

 Fitch in concluding that the excrescences are not of insect origin. He also claims to 

 have carefully watched the black-knot through all its stages from- its earliest com- 

 mencement to its complete maturity. He affirms that he bred from the galls five 

 distinct species of insects beside the curculio, but that not one of these could be con- 

 sidered a true gall-maker. Ho therefore very justly concludes that the excrescences 

 axe not of insect origin, but of fungoid origin ; and this conclusion, we may add, is 

 entirely in accordance with our own view of this subject. Our reasons for adoi)ting 

 this view are briefly these : 



1st. The excrescence itself is similar in structure to other excrescences which are 

 known to be of fungoid origin, and at the same time it is quite dissimilar to most 

 insect-galls produced in twigs and young branches. 



2d. The time of its development is opposed to the probability of its insect origin. 

 We are well aware that our knowledge of insect-galls is extremely limited, and that 

 here we are treading on dangerous ground, and may hereafter be obliged in our turn to 

 apologize to the entomologist ; but, so far as onr observations extend, insect-galls are 

 develoiied in the warmer seasons of the year, /. c, in spring, summer, and possibly early 

 autumn. Those that continue to be the domicile of tho young insect during the winter 

 are, so far as we have observed, fully grown in autumn, and do not increase in size the 

 following spring, a character which" does not hold good in the case of black-knot. 



3d. The fungus is always present with the excrescence, and its mycelium may be de- 

 tected even in tho earliest manifestation of tho tumor, and this fungus is never found 

 apart from tho black-knot. To our minds this alone is a sufiicient argument for our 

 belief in the fungoid oi-igin of the excrescence. Who ever heard of any undoubted 

 insect-gall being always accompanied and inhabited by a fungus ? On the other hand 

 the larvai of insects aro not always iireseut in the excrescence, and of those insects 

 that liave been bred from it, none, wo are told, have been true gall-makers. It is true, 

 members of the cynips family are gall-niakcrs, and the learned Schweinitz constantly 

 associated a cynips with his descriptions of this fungus, but then he did not afiirm 

 that the cynips produced the excrescence, and later investigators have failed to con- 

 firm his api^arent suspicions. Hence we do not think his mere association of the two 

 can have much weight either Avay. 



Like others, Avhose writings we have quoted, we also claim to have examined tho 

 black-knot carefully in its various stages of development, not entomologically, it is 

 true, but botanically, from which it is not unreasonable to suppose that wo may have 

 observed some details in its development which escaped their notice. We desire, 

 therefore, to express the results of our own observations, and wo desire this the moro 

 because in one or two points we cannot quite agree with the inferences and conclu- 

 sions of former investigators. 



If the smaller branches of a cherry-tree that is suffering from an attack of black- 

 knot bo carefully examined in November, some of them will be found to be slightly 

 swollen for a littlg distance immediately below the excrescences. Tlie cuticle of the 

 bark will bo cracked open liere and there, revealing tho soft tissues of the inner bai'k. 

 If a minute portion of this inner bark bo examined by tho aid of the microscope, 

 slender-jointed filaments or threads m.iy be seen, tliat liave insinuated themselves 

 among the bark-cells. These threads ore tho prinuiry vegetating condition of tho fun- 

 gus and are known to botanists as myccHnm. During the winter the enlargement of 

 the branch remains nearly or quite stationary, but with the advent of spring and tho 

 renewal of vegetable activity, the tumors increase in size, the chinks in the bark be- 

 come wider and more numerous, and, by the end of May, small dark-green stains are 



